A major challenge in the field of nanoelectronics is the preparation of nanoscale materials, including nanowires, as electrical conduits between the nanocomponents of such devices. Proteins, in particular amyloid fibrils, have received much attention in that they provide desirable structural characteristics and can be readily adsorbed onto a range of suitable substrates. While such features are attractive, the typically low conductivity levels of protein nanowires limit their application. Metallization has been considered, but under industrial conditions can be deleterious to protein structure and integrity.
As a result, the design and fabrication of useful nanoelectronic materials has been an on going concern in the art. One approach is suggested and illustrated by the production of orderly self-assembled nanostructures in nature. Many bacteria have the ability to assemble small protein subunits, termed pilins, into one or more extracellular structured fibers, pilus or pili. Members of the family Geobacteraceae, for instance, produce pili to facilitate cellular oxidation-reduction mechanisms.
Further, mechanisms for extracellular microbial Fe(III) reduction have long been of interest in the art. The oxidation of organic matter coupled to Fe(III) reduction has a substantial influence on the degradation of organic matter and the geochemistry of iron, trace metals, and nutrients in many soils and sediments. Furthermore, such Fe(III) reducers can play an important role in the bioremediation of subsurface environments contaminated with organic pollutants or with metals such as uranium.
Some microorganisms, such as Shewanella and Geothrix species, may transfer electrons from the cell to the iron oxide surface via excretion of soluble electron-shuttling compounds whereas others, such as Geobacter species, require direct contact with the oxide surface. Previous studies demonstrated that Geobacter metallireducens specifically produced pili during growth on Fe(III) oxide, but not during growth on soluble, chelated Fe(III). Childers, S. E., Ciufo, S. & Lovley, D. R. Geobacter metallireducens accesses insoluble Fe(III) oxide by chemotaxis. Nature 416, 767-769 (2002). However, it remains uncertain whether such structures can be used for electrical conductivity.